Help finding book series

I read a book a long time ago and can't remember the title. It has an agency that sends people back in time to make themselves powerful. The books all look forward to the time when the actual time arrives at the time when they began sending people back. The agency isn't portrayed as good, yet we follow several of the agents who are good people as they work from within to stop the agency. At one point they have genetically altered cro-magnons who are killers in the ancient past. There is something about Catalina Island that is important. I remember enjoying the books, but can't remember much else. Any help would be appreciated. Thanks